Connections to the power grid have radically changed over the past decade to include hybrid and battery-powered vehicles with large batteries. In addition, large batteries are sometimes used with alternative energy sources, e.g., solar panels. Plans to use energy storage with alternative energy sources that connect to the power grid are of interest to reduce dependence upon fossil fuels. Home batteries are proposed to provide the ability to send power from an alternative energy source back into the grid, for example.
Recently, plug-in electric vehicles (PEV) have surged in popularity. Currently, most PEVs establish connection to the grid only to recharge their batteries. But PEVs can also behave as distributed energy generators in the so called vehicle-to-grid (V2G) mode. See, W. Kempton, J. Tomic, S. Letendre, A. Brooks, and T. Lipman, “Vehicle-to-grid power: battery, hybrid, and fuel cell vehicles as resources for distributed electric power in California,” Institute of Trans-portation Studies, (2001). Researchers are exploring the capabilities of electric vehicles for peak power supply, renewable energy integration, regulation support and spinning reserve. Another group of research addresses novel applications such as reactive power compensation and current harmonic filtering. See, e.g. L. Drude, L. C. P. Junior, and R. Ruther, “Photovoltaics (pv) and electric vehicle-to-grid (v2g) strategies for peak demand reduction in urban regions in Brazil in a smart grid environment,” Renewable Energy, vol. 68, pp. 443-451, (2014); S. Han and S. Han, “Development of short-term reliability criterion for frequency regulation under high penetration of wind power with vehicle-to-grid support,” Electric Power Systems Research, vol. 107, pp. 258-267 (2014); S. Deilami, A. S. Masoum, P. S. Moses, and M. A. Masoum, “Real-time coordination of plug-in electric vehicle charging in smart grids to minimize power losses and improve voltage profile,” Smart Grid, IEEE Transactions on, vol. 2, no. 3, pp. 456-467, (2011).
The power grid is one of the most complex systems that mankind has engineered. Because the grid has no storage, electricity production must be continuously managed to meet the fluctuating demand. If this balance between generation and consumption is not maintained at all times, the system variables will start to drift from their nominal values. The ability to maintain frequency and voltage at their scheduled voltage is referred to as stability of the power system. Small disturbances, such as incremental load changes, are area of interest for steady-state stability. On the other hand, transient stability deals with large disturbances such as short-circuits and line trips. As PEVs increase in popularity and many are plugged into the grid simultaneously, the steady-state stability becomes more difficult to manage.
Scientists and engineers are constantly looking for new ways to improve the power grid stability using the concept of smart grid: smart control, smart demand response, smart management of HVDC lines and smart topology control. See, e.g., J. L. Rueda, W. H. Guaman, J. C. Cepeda, I. Erlich, and A. Vargas, “Hybrid approach for power system operational planning with smart grid and small-signal stability enhancement considerations,” Smart Grid, IEEE Transactions on, vol. 4, no. 1, pp. 530-539, (2013); A. Fuchs and M. Morari, “Placement of HVDC links for power grid stabilization during transients,” in PowerTech (POWERTECH), 2013 IEEE Grenoble, pp. 1-6, IEEE, (2013).
The main issue with most smart approaches concerns difficulties introduced by the reliance on a centralized entity that manages and controls a series of devices. This is also true for most PEV applications that also propose aggregating a group of vehicles to facilitate management, which adds yet another layer of security and privacy concerns, latency related problems and high initial cost.
Recently, we have shown that transient stability can be improved with PEVs. A. Gajduk, M. Todorovski, J. Kurths, and L. Kocarev, “Improving power grid transient stability by plug-in electric vehicles,” New Journal of Physics, vol. 16, no. 11, p. 115011 (Nov. 11, 2014). The control strategy proposed in this prior work of ours regulates power exchange between PEVs and the power grid, based on the average turbine speeds at conventional generators, in an effort to reduce the effects of large disturbances. The strategy modeled PEVs as loads. In certain moments their power may become negative and they will be perceived by the system as generators. It was shown that by regulating the power output of the PEVs, speed and voltage fluctuations during transients can be significantly reduced. Furthermore, the critical clearing time, that is the time to clear the fault which caused the disturbance, can be extended by 20 to 40%. This in turn yields a more robust power system.